Brecciation and chemical heterogeneities of CI chondrites

Nebular Versus Parent Body Processing

“…This evidence implies that fluid flow was essentially zero and that alteration occurred under isochemical conditions, a scenario that is most compatible with asteroidal alteration . This scenario is supported by the work of Morlok et al (2006), which shows that CI chondrites contain a diverse array of clasts with variable mineralogical characteristics and degrees of alteration. This diversity can only be reasonably explained by closed-system parent body alteration of starting materials with diverse initial compositions and mineralogy.…”

“…This conclusion is consistent with the old I-Xe ages for CI magnetites, which are almost certainly the product of aqueous activity (e.g., Kerridge and Bunch, 1979). Although it is possible that precursor components of the CI chondrites experienced preaccretionary alteration (Bischoff, 1998), it is clear that advanced and complex parent body alteration (e.g., Morlok et al, 2006) has completely obliterated any evidence of such processes.…”

“…CI chondrites are complex meteorites that consist of a dark, fine-grained matrix comprised of phyllosilicates with magnetite, sulfides, carbonates, and sulfates embedded within it (e.g., DuFresne and Anders, 1962;Nagy, 1966). They have experienced extensive brecciation on their asteroidal parent bodies that caused mixing of compositionally distinct lithic clasts on the millimeter to submillimeter scale Morlok et al, 2006).…”

Prebiotic carbon in clays from Orgueil and Ivuna (CI), and Tagish Lake (C2 ungrouped) meteorites

“…The amino acids in the CI meteorites, which differ from those in CM2 meteorites , suggests a parent body that was rich in cometary components such as water, ammonia, and HCN (Ehrenfreund et al 2001). Models of aqueous processing on the CI parent body call for multiple stages of alteration, though significant spatial mineral and element heterogeneity shows that equilibrium was not reached (Morlok et al 2006;Tomeoka and Buseck 1988). During the aqueous processing the smectite would be available to intercalate and modify soluble organics.…”

Chondrites and Their Components

“…The prominent sulfate veins in CI1 chondrites appear to have formed in fractures on Earth (Gounelle and Zolensky, 2001) and not in the parent body, so it is likely that aqueous solutions did not percolate through the rock. Third, CI1 chondrites are unique finegrained breccias as they are regolith breccias entirely composed of diverse, altered lithic fragments less than a few hundred micrometers in size (Morlok et al, 2006). They probably formed by alteration while they were brecciated in a very dynamic regolith Lee and Nicholson, 2009) and may represent samples of one or more icy asteroids that were thoroughly scrambled, gardened, and heated by impacts.…”